Leeds City Council's children's services department is not doing enough to safeguard young people, an Ofsted report has found.
The assessment by the education watchdog found the authority was one of 12 councils in England which was rated as performing poorly.
It found inadequacies in its systems for keeping children and young people safe from harm.
The council pledged to continue making improvements to children's services.
Ofsted said its findings were based on inspections of child care, schools, child protection services and safeguarding, and children's social care.
Twenty councils in England were found to provide excellent services, 77 were rated as performing well and 37 as adequate.
Ofsted chief inspector Christine Gilbert said: "The minority of councils that are performing poorly were put in this category primarily because they are not doing enough to keep children safe.
"Inadequacies have been identified in their approach to safeguarding children.
"These authorities know where improvements are needed and have plans in place to improve. There is much they can learn from the examples of those authorities that are performing well and excellently."
Director of children's services at Leeds City Council Nigel Richardson said: "Our staff have worked extremely hard over the past year to implement improvements to keep children and young people in Leeds safe from the risk of serious harm.
"However, we know that it will take time to see the full impact of theses improvements and we can still do more to build on this."
Councillor Judith Blake, the council's executive board member for children's services, added: "Since the last inspection we have implemented a full-scale review of children's services across the city.
"So it is very disappointing that the fantastic work that our staff and managers have done over the past year could not be taken into account."